But calving compactly has never been more important. Increased milk price volatility makes it even more critical that we maximise grazed grass in the diet. The change in growth rate over the last week shows how essential it is to have most of the herd at peak intake in order to take advantage of grazed grass from April on.

Occasionally farmers will quote the increased workload associated with calving half the herd in two to three weeks as being a negative of calving compactly. This is less of an issue where there are no herd health problems such as difficult calvings, mastitis or milk fever around calving time. The other factor is your calf rearing set up. Would small changes here make you more labour efficient during the calving season?

There are significant costs associated with poor fertility in grass-based dairy herds. These costs are magnified within an industry that has the potential to expand. A study by Teagasc and ICBF in 2014 used a model to simulate the overall economic effects of fertility at farm level.

The study quantified the economic effect of a number of key variables associated with reproductive inefficiency in a dairy herd and related them to a six-week calving rate for both cows and heifers. The variables used were increased culling costs, effects of sub optimum calving dates, increased AI and intervention costs and increased labour costs.

The effect of a change in each of the components was simulated in the model and the costs associated with each component were quantified. This was based on a milk price of 29.5c/l.

National data from ICBF was analysed over a four-year period. This was used to quantify the relationship between the six-week calving rate of a herd with survivability (percentage), calving interval (days) and the level of AI usage.

The overall objective was to create one single variable that explained the costs associated with infertility within a dairy herd. Each 1pc change in the six-week calving rate was associated with €8.22/cow/yr in the herd. Essentially improving the six-week calving rate from 65pc to 80pc is worth over €9,000 per year for an 80-cow herd.

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So what can you do at this stage to improve your six-week calving rate? Examine body condition score. The target herd average is to have cows at 2.9 body condition score at breeding. While it is late at this stage you can still have a positive effect by ensuring that cows are well fed coming up to the breeding season.

Concentrate

This means ensuring cows have enough good quality grass in their diet. Where grass supply is adequate, concentrate supplementation has no effect on fertility. But where grass supply is restricted then concentrate supplementation will improve reproductive performance.

Putting thin cows on once-a-day milking will also improve her chances of going back in calf, provided she is fed the same as those on twice-a-day milking.

Ensure the diet is properly balanced for energy, protein and minerals. Where supplementing cows on grass, high-fibre and low-protein ingredients such as soya hulls work well. Where a mineral deficiency is suspected you have two choices: feed the full minerals throughout the breeding season or do herbage and blood analysis in April to identify the mineral requirements of the herd.

Most farmers are slow to do pre-heats as they feel it is enough to concentrate on heat detection during breeding. But the benefits of knowing what cows are not cycling at the start of breeding are immense. Finding these problem cows after three weeks of breeding will give them very little chance of getting in calf in the first six weeks.

Some farmers will tail paint cows in the three to four weeks pre breeding and check the paint just twice a week, topping it up where necessary.

Improving your six-week calving rate by 15pc is difficult to pull off in one year but huge improvements can be made. Also bear in mind that choosing bulls now that are easy calving will help cows come back cycling quickly after calving next year.

Achieving a compact calving pattern is beneficial for herd management during the spring, will result in longer lactations, greater grass utilisation and increased profitability.

Nora O'Donovan is a Teagasc business and technology advisor based in Tralee, Co Kerry.